They might not all be to your taste but Metropolis in Ghostly Grooves (October 22) offers the Party Animal best bets in Tokyo on October 31, for Halloween 2009.
For the creative souls or those with a costume designer as a friend they suggest Ageha which they say hosts Japan's biggest Halloween party with "a costume contest with prizes ranging from cash to a Playstation 3—but be warned, contestants must have original costumes (no store-bought outfits allowed!). DJs include Taku Takahashi (m-flo) and Dexpistols. Trick-and-treaters get in for just ¥2,000, but if you come in civvies you’ll have to pony up ¥4,000."
Expats from down under or those wishing to hang out with an English speaking crowd can join the Aussie Halloween Party at Bar Quest, more subdued than Ageha it seems, Belly Dance Show...
Daring, C'est Bon Plage, a French Cafe at the Tobacco and Salt Museum (masthead below) will treat you to a 'pink' drink if you wear pink only (not sure if that means shoes as well).
Halloween 2009 in Japan for Tokyo Thursdays # 111